Atmospheric Pressure Chemical Vapor Deposition (APCVD) systems can be used to deposit, either On-Line, i.e. incorporated in a float glass line, or Off-Line, i.e., separate from a float glass line, one or more thin film layers of metal, metal oxide, metal nitrate and other materials at high deposition rates and at line speed v ranging typically from 0.1 m/min to up to 30 m/min onto large area glass substrates. In such APCVD thin film deposition systems, one or more deposition modules are arranged in a serial manner to deposit a given total thickness for each targeted thin film at a chosen line speed. Such APCVD systems can be used to deposit multi-layer films to produce Low-E glass used in the manufacturing of energy efficient (high reflection efficiently of infrared energy) windows, and/or for Transparent Conductive Oxide (TCO) coated glass sheets used for example as substrates for thin film photovoltaic and for display applications. One example of such an On-Line APCVD system can be found in U.S. Pat. No. 6,103,015 and an example of such an Off-Line APCVD system can be found in U.S. Pat. No. 4,595,634.
Other prior art Chemical Vapor Deposition (CVD) systems exist as well that operate either at Atmospheric Pressure (APCVD) or at Low (reduced) Pressures (LPCVD) and may or may not incorporate a continuously operated substrate transport mechanism to deposit at least one CVD thin film onto a wide range of thermally stable substrates. Examples of such thermally stable substrates are Si wafers, flat and bowed glass sheets, partially assembled thin film photovoltaic substrates, display substrates, metal, ceramic and plastic sheets or foils, graphite, carbon-carbon or ceramic tiles, etc. In related LPCVD systems the respective deposition modules are often also called shower heads or injector assemblies and all these names are intended to be used interchangeably in this patent.
During operation, the CVD deposition modules become sufficiently dirty as a result of CVD deposition process as to significantly affect the yield (pinholes and/or coating thickness uniformity) of the coated substrates. Thus, when a given defect threshold is exceeded, the CVD deposition process needs to be stopped because the system is no longer operating in a commercial viable mode. The respective CVD deposition modules must then undergo regular maintenance, i.e. they have to be moved offline, be cleaned, put back into their respective deposition position and reconnected to the process gas supply lines before the CVD deposition process can be resumed.
As a result of this regular deposition module maintenance time, the effective uptime, for example, of prior art On-Line APCVD systems are typically as low as 30-60% for optimum commercial viable system operations. Thus, the available system uptime due to regular deposition module maintenance directly affects the average cost per coated surface area. Further improvements that can minimize the CVD systems down time are therefore desirable.
In some prior art system, this deposition module maintenance frequency issue has sometimes been addressed by adding at least one additional process gas (for example a hydrocarbon gas to act a radical scavenger) to the process chemical mixture needed to achieve a target thin film thickness with a given CVD deposition process that reduces the reaction rate of the chosen process chemistry and allows the deposition process to be spatially more spread out and more uniform in the substrate movement direction. For example, U.S. Pat. No. 5,798,142 describes the influence of C2H4 on the deposition rate reduction of SiO2 for an APCVD method utilizing SiH4, O2 and N2 as primary APCVD process chemicals. While such prior art compensation methods can increase the deposition module maintenance interval, these methods typically also result in lower average deposition rates, lower process chemical utilization rates and/or limit which process chemistry can be used and/or which multi layer thin film design can produced on a given CVD deposition system. It can also require special (for example with longer deposition length) designed and manufactured CVD deposition modules to compensate for the lower and spatially more extended deposition area.
Two prior art APCVD deposition systems 30 used for On-Line APCVD deposition of thin films on float glass lines are summarized in FIG. 1. A float glass line 10 comprises a melting furnace 12, a tin bath 14, a high temperature annealing lehr 16 with an inside wall 17 and a low temperature annealing lehr 18 with an inside wall 19. Raw material enters the melting furnace 12 and a continuous sheet of float glass 20 exits the low temperature annealing lehr 18 of the float glass line 10 which is subsequently cut to required sizes and stored offline for later usages. To change the thickness of the glass sheet 20, among others, the line speed v of the float glass line 10 need to be adjusted: for example, 2× thinner glass sheet 20 manufacturing requires approximately a 2× faster line speed v and/or a mass throughput change to the melting furnace 12.
Numbers with a letter “T” or “L” attached indicate that the respective component of the APCVD system is from an APCVD system having an On-Line Deposition Position (deposition position) inside the tin bath 14 section (“T”) or in the high temperature annealing lehr 16 section (“L”) of the float glass line 10. Numbers without a letter attached represent a generic component with no significant distinction of where the respective component is located on a float glass line 10 and/or include equivalent Off-Line CVD systems. The deposition module 32 moves on a motion control system, for example shown in FIG. 1 as a Rail System (rail system) 34 oriented in the X-axis direction, i.e. perpendicular to Z-axis of the float glass line 10, also defined as the direction in which the glass sheet 20 or a respective flat substrate or substrate group moves. The prior art rail system 34 has two principal stop locations: one is at the inline deposition position 36, i.e. over the middle of float glass line, and the other is at the offline maintenance position 38 located on one side (right side shown in FIG. 1) of the float glass line 10 where the deposition module 32 is first fully cooled down and then cleaned, serviced and/or maintained.
For prior art Off-Line CVD systems (not shown in FIG. 1), the deposition module is moved offline, i.e. to the left or right of the Off-Line system's Z-axis and reinserted from the same side after having been cleaning. Typically, mechanical registration means are used to deliver a respective deposition module 32 back to the deposition position 36.
Eventually each deposition module of a CVD coating system needs to be serviced to prevent yield problems due to excess particulates falling from more and more polluted sections of the deposition module onto the substrate or substrates underneath. With the prior art solutions the CVD system design and operation balance requirements (to obtain commercial viability) between system cost, maintenance cost, chemical utilization cost, available space on a given process line, etc. limit the lowest achievable cost for a given high volume (high surface area) CVD system.
Thus, there is a need in the art for a solution which allows for increased process uptime and overall cost reduction per coated substrate surface area in high volume production.